1. Field of the Invention
The present invention generally relates to devices for marking, locating and tracing obscured conduits, and more particularly to a probe or sonde which has a separable case and inner shell, facilitating repair and replacement of components including the battery and transmitter assembly.
2. Description of the Prior Art
Probes have been used for many years to trace obscured conduits, such as underground pipes for water, wastewater, gas, etc. For example, construction workers trace the path of the conduit in order to avoid it during excavation. It is also necessary to locate conduits from time to time for repair or other maintenance. These probes, also referred to as sondes, are provided at different frequencies to accommodate various types of receivers, typically operating at 512 Hz, 8 kHz and 33 kHz, either continuous or pulsed. The outer dimensions commonly range from a few millimeters in diameter and a few centimeters in length, to a few centimeters in diameter and half a meter in length.
As shown in the prior art illustration of FIG. 1, the sonde is placed in the conduit at an access point, and is forced through the conduit by a rod or shaft. The rod is flexible enough to store and dispense from a reel above ground, but it is sufficiently rigid to push the sonde through the conduit. A craftsperson using a receiver follows the sonde above ground, marking the surface to delineate the underground path of the pipe. The transmitter of the probe may be modified for various purposes as discussed in U.S. Pat. No. 3,597,680.
One problem with prior art sondes is the incorporation of the electronics (transmitter) as a permanent part of the outer protective case. The outer case is a costly component since it must service hostile environments such as water, sharp edges in broken pipe, and ground entrapped hydrocarbon solvents that attack low cost polymeric materials. For example, the '680 patent refers to the expensive material sold as DELRIN by E. I. duPont de Nemours and Co. A complete sonde can consequently cost several hundred dollars. Yet, since the transmitter is potted or affixed to the inside of the case, the sonde can become essentially worthless if the transmitter breaks down. Moreover, when there is a need to change the frequency of the transmission signal or its modulation method, the present systems all require total replacement of the device. The present units are also essentially non-repairable, although the battery may be salvageable.
It is possible, but very problematic, to provide power to a sonde via the push rod, so all commercially available sondes are battery powered. Many sondes require battery replacement after as little as six hours of use. Custom batteries as well as standard 1.5 volt or 9 volt batteries are used. A second problem with prior art sondes relates to the manner is which the battery is placed inside the case. When the cap of the sonde is removed from or attached to the housing, by screwing it off or on, the cap engages one end of the battery and causes the leads thereof to twist and become entangled, often damaging them to the point where they are non-repairable, i.e., the entire sonde is again worthless. It would, therefore, be desirable and advantageous to devise a sonde which allows multiple electronic modules to be used with the same outer casing, and which does not damage the battery leads during disassembly or re-assembly of the sonde casing.